Direct Current (DC) Power Supply devices are broadly used in various electric equipment such as wireless phone, walkman, radio receiver, modem, charger, Liquid-crystal display (LCD) and so on, and all these electric equipment need DC power supply (DC transformer) supplying power.
Conventional DC transformer is just a simple AC (alternating current)—DC transforming circuit, which is connected with an AC power outlet and supplies power to electric device loads with a constant voltage. Such transformer can supply power to only one electric device load. However, each electric device load has its own power which is different from other type, so that a user must equip several DC transformer if he has more than one electric device load, and the user must remember corresponding relationship between electric device loads and DC transformers. It is difficult to use especially for those who are not familiar with electric knowledge. And the electric device loads will be soon damaged if the user connects a DC transformer with a unfit device.
When an electric device load supplied by DC transformer is damaged or abandoned, the corresponding DC transformer will be abandoned too. A lot of such abandoned DC transformers produce serious environmental problem.
Besides, manufacturers which produce DC transformers or electric device loads must manufacture a lot of different DC transformers according to different electric device load specifications. It is difficult for manufacturer to save cost and working time.
At present, there is a charger equipped with a simply commutating and transforming circuit which can supply power at different voltage under user's handle. Such design needs a user to select a voltage value before connecting the charger to an electric device load, it is ineluctable to damage the electric device loads while user select a wrong voltage value.
Moreover, many countries have their own design specification in electrical outlets and plugs, users especially to those who often travel abroad meet the question that his plug can not fit for the outlet supplied by hotel, and the like. Such as, he has a notebook equipped with a two pin plug but the outlet has three hole, and he can not use his notebook finally.